Difunctionalisation of Urea-Containing Alkenes by Radical Methods

  • Roman Abrams

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Chapter one of this thesis details the development and scope of conditions for the photoredox catalysed alkyl-arylation and aryl-phosphorylation of vinyl ureas, by use of alkyl sodium sulfinate and diarylphosphine oxide radical precursors. This alkene difunctionalisation process makes use of an organophotocatalyst, allowing the reaction to be driven by visible light. The afforded α-tertiary urea products can be simply converted into their respective α-tertiary amines by solvolysis.

This difunctionalisation process has been probed mechanistically using a suite of methods, which together imply the presence of a reductive quenching photoredox cycle and the formation of α-metallated urea intermediate that undergoes N to C intramolecular arylation across the urea tether.

Chapter two of this thesis explores an approach based on the aminative cyclisation of allyl ureas and allyl carbamates using photoredox catalysis to generate amidyl radicals by proton-coupled electron-transfer (PCET). However, instead it was discovered that the azo-cycloamination of allyl ureas and carbamates could be conducted in the absence of photocatalyst and light, by simple exposure of certain olefinic starting materials to aryl diazonium salt in the presence of phosphate base. The resulting azo compound products were amenable to deprotection steps, such as hydrogenation of the azo bond to a primary amine.

Preliminary mechanistic investigation of this azo-cycloamination were conducted and comprised of radical trapping experiments and cyclic voltammetry analysis. These experiments imply the presence of a radical-chain process initiated by formation of aryl radical and propagated by PCET N-H homolytic activation.
Date of Award21 Jan 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJonathan P Clayden (Supervisor)

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